Method of refining metals



` June 16, 1959 K, 1 KORPl ET AL 2,890,952

METHOD oF REFINING METALS Filed Nov. 4, 1955 CARBON fa/PE J2 l l 10 PULVEAIZER PdLVEF/Zfl? Marilou or aanname METALS Karl J. Korpi, Altadena, Calif., and Raymond C. Johnson, New York, NX., assignors to The Lummus Company, New York, NX., a corporation of Delaware Application November 4, 1955, Serial No. 544,914

4 Claims. (Cl. 75-84.1)

This invention relates to the production of high melting point metallic elements and has for an object the provision of an improved method or process for producing highspurity refractory metals. More particularly, the invention contemplates the provision of an improved method or` process for producing high-purity, high melting point metallic elements by the dissociation of subhalides of such elements.

This application relates to our copending application Serial Number 543,514, led October 28, 1955, and entitled Method of Refining Metals.

Metals such as titanium, zirconium, thorium, tungsten, hafnium, vanadium, molybdenum and uranium, etc., have become important commercial materials in view of the unusual properties which they exhibit. At present, there are several ways of recovering such metals all of which are complicated and expensive. For instance, the procedures now used for the manufacture of titanium are the following:

(l) Reduction of titanium tetrachloride or other titanium tetrahalide with either sodium or magnesium with subsequent elimination of the sodium or magnesium halide which is formed hy washing or distillation.

(2) Reduction of titanium oxide with calcium hydride at elevated temperature. This procedure has not been too successful since the product is always heavily contaminated with oxygen.

(3) Thermal dissociation of a titanium tetrahalide on a hot lament under vacuum.

(4) Electrolytic recovery from fused salts.

At the present time, the most widely used commercial method is the reduction of titanium tetrachloride with magnesium or sodium followed by subsequent distillation of the magnesium chloride or sodium chloride by product in a vacuum. This process', popularly referred to as the Kroll process, is inherently expensive since it produces a titanium halide from a titanous ore and then reduces the halide with another substantial-1y pure metal. In such a process, the necessary expense of the pure secondary metal establishes a very high minimum cost. Also the titanium is formed as a metallic sponge which necessitates further processing to obtain the metal in a useable form.

As indicated, titanium, as well as the other aforementioned metals, have many unusual physical and chemical properties. In order to be workable and generally useful, these metals have to -be supplied in an extraordinarily pure form. Small percentages of oxygen, nitrogen, hydrocarbon or carbon embrittle the metal markedly so that it cannot he handled fby metal working procedures. Under these conditions, great care is taken to eliminate these undesirable elements from being present while thje metal is being formed. While the above noted processes are illustrative of titanium recovery, they are in principal applicable to other metal recovery in pure es am elemental form. 'I'hese processes usually involve the recovery of crystalline metals in the form of extremely small particles or a sponge form of metal. The small particles are inherently unstable and even pyrophon'c, readily oxidizing in the presence of air or water, and even react with nitrogen from the air to form nitrides of the metal.

Other diliiculties with the treatment and recovery of these metals result from their high melting point. The property of titanium, in the molten state, of acting as a nearly universal solvent presents a major problem in handling the metal in such a state. Almost all of the impurities tolerable in other materials reduce the ductility of the high melting point metals to the degree of being unworkable.

To illustrate our process of producing high purity, high melting point, metallic elements we have hereinafter described our invention with regard to the treatment and recovery of titanium.

In accordance with the present invention, the metal titanium is produced as a relatively high purity product of the little known reaction of titanium monoxide with the titanium halides. Although the reactions of decomposition of sub-halides to metal and higher halides has been known, the possibilities of combined titanium halide reactions have not been appreciated. Through our invention pure ductile titanium is produced in plate or ingot form, rather than in oxidizable crystals or sponge form, and at a cost substantially below that of present day methods. Further, our invention provides a relatively low temperature process which can operate at substantially atmospheric pressure with a minimum of heat input and without the need for hydrogen or other costlyV reducing materials such as sodium or magnesium. Other objects and advantages of our invention will appear from the following description of one form of embodiment taken in connection with the attached drawing which is a simplied ow diagram of the reaction according to the invention.

In view of the various metals recoverable and variations of equipment which may be used to carry out our process, the ow diagram is to be considered of generally informative nature and illustrative of process steps rather than a limitation as to a specic metal or type of apparatus.

Accordingly, in our method, titanium Ibearing ores such as rutile, ilmenite and titanite or titanium dioxide-bearing slag obtained as a result of the smelting of titaniferous iron ore, are charged to pulverizer 10. These ores or slag, even in their purest state, contain iron, silicon and aluminum as regular impurities. Alkaline earth metals,

such as calcium, are likewise commonly found in variousV We reduce the titanium dioxide ofv titania rich ores. such ores with powdered carbon supplied to pulverizer 12 and produce titanium contaminated with lower oxides including Ti305, Ti203 and TiO, and titanium carbide V in furnace 14. The reducing agent fed to pulverizer 12 may be derived from any known carbon source; however,

of carbon monoxide and carbon dioxide, thereby reduc- Y ling the titanium dioxide to titanium. Some of the carbon may react with the titanium dioxide to form titanium carbide and carbon monoxide and carbon dioxide. `To prepare titanium in furnace 14, we have used a mixture of lparts by Weight of crushed rutile and 27 parts` by 4Weight of crushed petroleum coke, consolidated byprese I sure to a dense solid. Analysis of the rutile and petroleum coke used by us indicated the following:

The furnace 14 may be an electric resistance furnace or it may be of any typical arc, cupola or fluidized design. In the furnace, the titanium dioxide is reduced by carbon by a series of step-wise reactions to produce lower oxides of titanium, elemental titanium, and titanium carbide in accordance with the following chemical equations:

A mixed product of TiO and TiC may be obtained in furnace 14 by carrying out the reaction at a temperature of 900-1l00 C. In presence of excess carbon, titanium carbide will be the favored product near 1000 C. at atmospheric pressure according to reaction 3. However, it is desired to make the maximum of metal and a minimum of carbide and lower oxides, hence the furnace must be lheated to from l500-2l00 C. with the proper carbon ratio to promote reactions 2 and 5. The carbon monoxide and dioxide formed during reduction is driven olf under suitable conditions through line 16.

Products of the furnace other than carbon monoxide and carbon dioxide are cooled to about 700 C. and are in the form of a fused agglomerate containing titanium, titanium carbide and titanium monoxide plus impurities such as small amounts of iron, chromium, vanadium and silicon. The material is ground or pulverized in pulverizer 18 for further handling.

The pulverized titanium-titanium monoxide mixture is then charged to reactor 20, which is operated under conditions to exclude oxygen, nitrogen and moisture. This reactor is preferably maintained at a temperature of between 600 C. and 8700 C. and at substantially atmospheric pressure. Under the conditions of elevated temperature and controlled atmosphere, the pulverized crude titanium mixture introduced to the reactor is subjected to the action of a higher metal halide vapor entering through line 22 so that an exothermic reaction results. The reaction in reactor 20 is so exothermic in nature that only enough heat to start up is needed from an external source. The temperature within the reactor is controlled by the amount of halide vapor input through line 22.

We have found that any of the halides which readily combine with titanium may be used to form the halide vapor entering reactor 20 through line 22. Principally we have formed metallic titanium according to our process using iodine or chlorine, as examples of the halogens, to form the titanium halides. It is obvious 4 that bromine may also be used to form the titanium halide.

For the purposes of explanation, the halide portion of compounds illustrated in the following reactions is noted by the symbol X and represents any of the aforementioned elements in the halide group.

The vapor in line 22 is principally titanium tetrahalide (TiX4) but in some cases may include equilibrium amounts of lower halides and upon reaction with the titanium mixture charged to reactor 20 forms liquid titanium dihalide (TiXz) which is removed through line 24.

The titanium higher halides function somewhat in the manner of carriers in accordance with reactions illustrated by the following equations:

The titanium oxides and carbide present in the reactor charge that do not react with the higher halides under the aforementioned conditions, remain behind in the reactor as impurities. Depending upon the relative densities of the varied impurities and the particular dihalide used in the process, these impurities will either sink or oat. Those that float can be skimmed olf the top of the liquid dihalide through line 26, while those that sink can be removed from the bottom as sludge through line 28. The dihalide formed can be removed from near the middle of the liquid layer through line 24.

The impurities of line 28, comprising mainly titanium carbide and titanium monoxide, can be introduced into an auxiliary reactor for further reaction to produce lower halides of titanium according to the following equations:

Both of these reactions are favorable at temperatures below about 500 C.; hence such auxiliary reactor should be operated at about 400 C. while the tetrahalide vapor is introduced. This reactor should be operated batchwise so that after charging and reacting the solid titanium carbide and titanium monoxide with the tetrahalide vapor, such reactor is then heated to from 600 C. to 700 C., which is the melting point range of dihalidesl of titanium. Under these conditions, the trihalides, decompose to dihalides and tetrahalides and the liquid dihalides may thereafter flow through line 124 to reactor 30 to join the ow of liquid dihalides in line 24. The tetrahalide vapors may remain in the auxiliary reactor to react with a fresh charge of titanium carbide and titanium monoxide at the lower temperatures with additional tetrahalide added as required.

The liquid titanium `dihalide (TiXz) removed from reactor 20 through line 24 is then charged to a second reactor 30 which contains a plurality of electric heating elements generally indicated at 32. Each heating element is enclosed in a titanium sheath 34 and is maintained at a temperature of from 800 C. to 1150 C. The liq-uid titanium dihalide pool within reactor 30 is heated by the sheathed heaters to an average temperature of between 600 C. and 800 C. and in this temperature range, the titanium dihalide is thermally decomposed to form elemental or metallic titanium, which deposits on the titanium sheaths or collectors in a high state of purity, and to titanium tetrahalide.

The decomposition of titanium dihalide to yield metallic titanium is according to the following equation: (1o) 2TiX2 Tir-Tix.1

(liquid) (solid) (gas) Any titanium trihalide which may be present is generally unstable and dissociates into titanium dihalide and titanium tetrahalide. The tetrahalide and some of the unreacted dihalide formed during the thermal decomposition in reactor 30 is in a gaseous state and is removed through line 36 and pumped by pump 38 to condenser 40. In .condenser 40, the gaseous mixture is 'cooled to a point whereby any titanium dihalide -is condensed for return to reactor 30 in line 42 while the gaseous titanium tetrahalide is recirculated to line 22 through line 44 andprovides substantially all of the tetrahalide requirement of reactor Z0. a After the initial starting up of our process, the halide used for reacting with titanium proceeds in continuous circulation between reactors Z0 and 30.. Only a small amount'of tetrahalide is necessary as make-up since the halide circuit is substantially closed with only small amounts of halide loss through the formation o f Volatile halides of the metallic impurities in the raw material. The volatile-halides areremoved through line 46 to condenser 48 where the tetrahalide is condensed and returned through line 46 to reactor 20. The volatilehalides are then removed from the system through line 50.'

Within the reactor 30 there is a continuous deposition and growth of titanium on the heater sheaths 34 whereby they obtain the form of an ingot. Periodically the sheaths are removed and form the pure titanium product after which a new sheath is placed over the heating element and returned to the liquid pool of titanium dihalide.

Around each heater sheath is a refractory thermal barrier 52 which acts to substantially shield the liquid dihalideppool from the higher temperature of the heater while at the same time directs theliquid dihalide in recirculating llow past the sheath for dissociation at the heated sheath temperature. k ln some instances the heating elements may also be maintained` v in the vapor phase over the liquid in reactor 30 as for example where it is found that the par- ,.'cularvtitanium dihalide used decomposes more rapidly asavapor.. p w,

`To illustrate the actual operating conditions of the deposition of highly pure titanium, the following examples are submitted.

Example I Metallicdor. elemental titanium was deposited in solid ingot form onl a sheathed heater immersedin `titanium diiodide (Tilg).

Vaporous titanium tetraiodide at a temperature in the neighborhood of 380 C. was passed into contact with a bed of crushed slag comprised of lower titanium oxides, titanium, titanium carbide and small amounts of impurities. The crushed slag was maintained at a temperature in the neighborhood of 650 C. The titanium tetraiodide rapidly reacted with the slag to form titanium diiodide,

"the diiodide forming a liquid pool at a point removed from the slag bed. 'Ihe liquid titanium diiodide, maintained at a temperature of about 750 C., dissociated on the surface of the heated sheath to form elemental titanium which continually coated on the sheath immersed within the pool and kept at about 950 C., and titanium tetraiodide vapor which was continually withdrawn from the space above the pool.

When the sheath, with the elemental titanium deposited thereon was withdrawn from the pool and weighed, it was found that substantially all of the titanium by weight originally in the slag bed had been deposited on the sheath.

Example Il Metallic or elemental titanium was deposited in solid ingot form on a sheathed heater immersed in titanium dichloride (TiClg).

Vaporous titanium tetrachloride at a temperature in the neighborhood of 700 C. was passed into contact with a bed of crushed slag comprised of lower titanium oxides, titanium, titanium carbide and small amounts of impurities. The crushed slag was maintained at a temperature in the neighborhood of 725 C. The titanium tetrachloride rapidly reacted with the slag toform titanidichloride, the dichloride forming a liquid pool at a point removed from the slag bed. The liquid titanium dichloride, maintained at a temperature of about`750 C., dissociated on the surface of the heated sheath to form elemental titanium which continually coated on the sheath immersed within the pool and kept at about 1l00 C., and titanium tetrachloride vapor which was continually withdrawn from the space above the pool. i When the sheath, with the elemental titanium deposited thereon was withdrawn from the pool and weighed, it was found that substantially all of the titanium by Weight originallyl in vthe slag bed had been deposited on'the sheath. y a

Having now described our invention with regard to the production of elemental titanium and having given examples to illustrate modifications of our process, v'we desire a broad interpretation of the invention as applicable to the production of high melting point metals within the scope of the disclosure herein and the following claims.

:We claim: 1. The method of producing a metal selected from the group consisting of titanium, zirconium, hafnium, thorium, tungsten, vanadium, molybdenum and uraniumby the disproportionation of an unsaturated halide of the metal, which comprises halogenating a crude mixture of said metal with a saturated halide of said metal, the

halogen component of which is selected from the group.

consisting of chlorine, iodine and bromine, eiecting said halogenation in a first reaction zone at substantially atmospheric pressure and at from about 600-870" C. thereby to form an unsaturated halide of said metal and im purities comprisingmetallic oxides and carbides, withdrawing said impurities from said first reaction zone and introducing them into an auxiliary reaction zone for halogenation therein, effecting said halogenation in said auxiliary reaction zone at substantially atmospheric pressure andl at from aboutl E350-500 C. thereby to form additional unsaturated halide of said metal, withdrawing said unsaturated halide as a liquid from said reaction zones and introducing it into a second reaction zone for Vdisproportionation therein to said metal and a saturated` halide of said metal, eifecting said disproportionation in said second zone at substantially atmospheric pressure and at from about G-1150 C. in the presence of a body of said metal, depositing disproportionated metal on said body and recirculating the saturated halide formed during disproportionation to said rst and auxiliary re action zones for accomplishing said halogenation therein.

2. The method of producing a metal selected from the group consisting of titanium, zirconium, hafnium, thorium, tungsten, vanadium, molybdenum and uranium by the disproportionation of an unsaturated halide of the metal, which comprises halogenating a crude mixture of said metal with a saturated halide of said metal, the halogen component of 'which is selected from the group consisting of chlorine, iodine and bromine, effecting said halogenation in a rst reaction zone at substantially atmospheric pressure and at from about 60G-870 C. thereby to form an unsaturated halide of said metal and impurities comprising metallic oxides and carbides, withdrawing said impurities from said first reaction zone and introducing them into an auxiliary reaction zone for halogenation therein, effecting said halogenation in said auxiliary reaction zone at substantially atmospheric pressure and at from about S50-500 C. thereby to form additional unsaturated halide of said metal, withdrawing said unsaturated halide as a liquid from said reaction zones and introducing it into a second reaction zone for disproportionation therein to said metal and a saturated halide of said metal, elfecting said disproportionation in said second zone at substantially atmospheric pressure in the presence of a body of said metal by forming a pool of said liquid unsaturated halide around said body and maintaining said pool temperature at from about 600- 800 C. and said body temperature at from about 800- 1150" C., depositing disproportionated metal on said body, and recirculating the saturated halide formed during disproportionation to said first and auxiliary reaction zones for accomplishing said halogenation therein.

3. The method of producing a metal selected from the group consisting of titanium, zirconium, hafnium, thorium, tungsten, vanadium, molybdenum and uranium by the disproportionation of an unsaturated halide of Ithe metal, which comprises halogenating a crude mixture of said metal with a saturated halide of said metal, the halogen component of which is selected from the group consisting of chlorine, iodine and bromine, eiecting said halogenation in a first reaction zone at substantially atmospheric pressure and at from about 600-870 C. thereby to form an unsaturated halide of said metal and impurities comprising metallic oxides and carbides, Withdrawing said impurities from said first reaction zone and introducing them into an auxiliary reaction zone for halogenation therein, electing said halogenation in said auxiliary reaction zone at substantially atmospheric pressure and at from about 350-500 C. thereby to form additional unsaturated halide of said metal, withdrawing said unsaturated halide as a liquid from said reaction zones and introducing it into a second reaction zone for disproportionation therein to said metal and a saturated halide of said metal, effecting said disproportionation in said second zone at substantially atmospheric pressure in the presence of a heated body of said metal by forming a pool of said liquid unsaturated halide around said body and maintaining the liquid in said pool at a temperature of from about 600800 C. by circulation over said body, said body being maintained at a temperature of from abou-t 800-1150 C., depositing disproportionated metal on said body, and recirculating the saturated halide formed during disproportionation to said iirst and auxiliary reaction zones for accomplishing said halogenation therein.

4. The method of producing titanium by the disproportionation of titanium dihalide, which comprises halogenating a crude mixture of titanium with titani tetrahalide, the halogen component of. which is selected from the group consisting -of chlorine, .iodine and bromine, effecting said halogenation ina lirst reaction zone at substantially atmospheric pressure .and at from about 600-870V C. thereby to form titanium dihalide and impurities comprising titanium oxides and carbides, withdrawing said impurities from said reaction zone and introducing them into an auxiliary reaction zonefor halogenation therein, effecting said halogenationin said auxiliary reaction zone at substantially atmospheric pressure and at from about S50-500 C.V thereby to form additional titanium dihalide, withdrawing said titanium dihalide as a liquid from said reaction zones and introducing it into a second reaction zone for Ydisproportionation therein to titanium and titanium tetrahalide, eiecting said disproportionation in said secondzone at substantially atmospheric ypressure andat from about 800- 1l50 C. in the presence of a solid body of titanium, depositing disproportionated titanium on said body and recirculating the titanium. tetrahalide formed during disproportionation to said rst and auxiliary reaction zones for accomplishing said halogenation therein.

References Cited in the le of this patent UNITED STATES PATENTS 2,670,270 Jordan Feb. 2s, 1954 2,694,652 Loonam Nov. 16, 1954 2,706,153 Glasser Apr. 12, 1955 2,720,445 Ruehrwein et al. Oct. 11, 1955 2,745,735 Byrns May 15, 1956 FOREIGN PATENTS 722,901 Great Britain Feb. 2, 1955 723,879 Great Britain Feb. 16, 1955 OTHER REFERENCES Mellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 7, pp. l0, 1l, 27, 74, 75, 76; publ. 1926.

Barksdale: Titanium, pp. 4l, 42; publ. 1949.

Steel, July 24, 1950, pp. 63, 64, 76. 

1. THE METHOD OF PRODUCING A METAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM, ZIRCONIUM, HAFNIUM, THORIUM, TUNGSTEN, VANADIUM, MOLYBDENUM AND URANIUM BY THE DISPROPORTIONATION OF AN UNSATURATED HALIDE OF THE METAL, WHICH COMPRISES HALOGENATING A CRUDE MIXTURE OF SAID METAL WITH A SATURATED HALIDE OF SAID METAL, THE HALOGEN COMPONENT OF WHICH IS SELECTED FROM THE GROUP CONSISTING OF CHLORINE, IODINE AND BROMINE, EFFECTING SAID HALOGENATION IN A FIRST REACTION ZONE AT SUBSTANTIALLY ATMOSPHERIC PRESSURE AND AT FROM ABOUT 600-870*C. THEREBY TO FORM AN UNSATURATED HALIDE OF SAID METAL AND IMPURITIES COMPRISING METALLIC OXIDES AND CARBIDES, WITHDRAWING SAID IMPURITIES FROM SAID FIRST REACTION ZONE AND INTRODUCING THEM INTO AN AUXILIARY REACTION ZONE FOR HALOGENATION THEREIN, EFFECTING SAID HALOGENATION IN SAID AUXILIARY REACTION ZONE AT SUBSTANTIALLY ATMOSPHERIC PRESSURE AND AT FROM ABOUT 350-500*C. THEREBY TO FORM ADDITIONAL UNSATURATED HALIDE OF SAID METAL, WITHDRAWING SAID UNSATURATED HALIDE AS A LIQUID FROM SAID REACTION ZONES AND INTRODUCING IT INTO A SECOND REACTION ZONE FOR DISPROPORTIONATION THEREIN TO SAID METAL AND A SATURATED HALIDE OF SAID METAL, EFFECTING SAID DISPROPORTIONATION IN SAID SECOND ZONE AT SUBSTANTIALLY ATMOSPHERIC PRESSURE AND AT FROM ABOUT 800-1150*C. IN THE PRESENCE OF A BODY OF SAID METAL, DEPOSITING DISPROPORTIONATED METAL ON SAID BODY AND RECIRCULATING THE SATURATED HALIDE FORMED DURING DISPROPORTIONATION TO SAID FIRST AND AUXILIARY REACTION ZONES FOR ACCOMPLISHING SAID HALOGENATION THEREIN. 